Tough denture and method for producing the same

ABSTRACT

The present invention provides a tough denture and a method for the production, which comprises solid PMMA as a main component, being added polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber, and is fabricated in a process of being mixed and injected into a denture mold.  
     PMMA denture of present invention shows improving safety to living organism and productivity of molding because of excellent mechanical properties and remarkable elution volume decrease after polymerization in comparison with ordinary type denture of heat-polymerized PMMA. Furthermore, it is possible to widely apply to clinical use because of good adaptability in oral and economical advantage.

BACKGROUND of THE INVENTION

[0001] 1. Field of The Invention

[0002] The present invention relates to tough denture fabricated of injectionable polymethyl-metacrylate (PMMA) and a method for producing the same. The denture in this invention includes partly or whole artificial tooth, and an artificial tooth base.

[0003] 2. Description of The Related Art

[0004] Present dentures employed in clinical, are known a heat-polymerized type PMMA, injection-type polysulfone (PS) and polycarbonate (PC) resins. The heat-polymerized type PMMA is fabricated of a mixture of methyl-metacrylate (MMA) monomer liquid and PMMA pre-polymer powder by mixing and heat-polymerizing in a denture-shaped mold. However, there are several product drawbacks in this method, namely, unstable shape caused by high shrinkage of polymer during polymerization, poor mechanical properties such as impact resistance and toxicity of living organism that is pointed out to cause an allergy by dissolving a lot of monomer residue after polymerization.

[0005] Because of the above drawbacks, PS and PC are employed as injectionable denture materials instead of the heat-polymerized type PMMA. However, PS shows poor impact resistance and PC shows toxicity and environmental pollution of bis-phenol A remained as monomer residue, and poor adhesion to mending material of PMMA that is difficult to improve.

[0006] Although it is eager in dental field to invent and apply a novel denture that shows excellent mechanical properties including impact resistance and has a few monomer residues, however there is still no PMMA denture to meet above conditions.

[0007] The theme which confronts us is to invent the excellent denture fabricated of PMMA and a method for the production, having a few monomer residue including the bis-phenol A, dissolved in one's mouth, and showing excellent mechanical properties including impact resistance.

SUMMARY OF THE INVENTION

[0008] The present invention provides a tough denture and a method for the production, which comprises solid PMMA as a main component, being added polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber, and is fabricated in a process of being mixed and injected into a denture mold.

[0009] Term of “toughness” in the present denture means that tensile and Izod impact strengths are more than 75.0 MPa and 1.62 kg·cm/cm², and bending strain at 5.0 kgf is less than 3.00 mm. Furthermore, elution volume from monomer residue after PMMA polymerization is less than 3% in the invented denture.

DETAILED DESCRIPTION OF THE INVENTION

[0010] PMMA of the present invention is possibly employed not only pure syndiotactic PMMA used in general industry, but also a blend of syndiotactic and atactic PMMAs in order to improve mechanical and thermal properties by forming stereo complex.

[0011] The higher tacticity of the PMMA blend composed of the both PMMA s, the better. The tacticity is preferably more than 60%, more preferably more than 80%. Blend ratio of both PMMAs is preferable in a range of 40-60% to 60-40% in order to form stereo complex, in spite of a fact that the ratio is freely changed. A weight-average molecular weight of PMMA for the invented denture, in both phases, is preferable in a range of 100 to 300 thousand, more preferable in a range of 120 to 250 thousand. Because PMMA denture having the weight-average molecular weight of less than 100 thousand shows poor mechanical properties in spite of a fact that it easily injects. Therefore, PMMA having weight-average molecular weight of more than 100 thousand is preferable.

[0012] Although PMMA of high weight-average molecular weight is preferable in a view of mechanical properties, however uniform-shaped denture is difficult to fabricate from PMMA having weight-average molecular weight of more than 300 thousand, because it shows poor fluidic and then poor injectionable as a result of high melt viscosity.

[0013] PMMA of present invention is added polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber in order to improve the mechanical properties, namely toughness. This process can be applied to not only pure syndiotactic PMMA, but also the blend of syndiotactic and atactic PMMAs in order to form stereo complex.

[0014] The polyacrylate rubber co-polymer is composed of alkyl acryl ester and cross-linkable vinyl monomer. Here, the alkyl acryl ester includes acryl methyl, acryl ethyl, acryl propyl, acryl i-propyl, acryl n-butyl, acryl i-butyl, acryl t-butyl, acryl n-hexyl, acryl octyl, acryl 2-ethylhexyl, and acryl lauryl. Especially, acryl ethyl, acryl n-butyl and acryl 2-ethylhexyl are preferable because those compounds show low Tg of −22, −54 and −85° C., and then good elasticity.

[0015] The cross-linkable vinyl monomer includes 2-chroloethyl-vinyl-ether, acryronirile, glycidyl-metacrylate and acryl-glycidyl-ether. And the monomer is co-polymerized in a range of 5 to 20% with the above alkyl acryl ester.

[0016] The alkyl acryl ester of the methylmatacrylate-alkylacrylate-styrene ter-polymer includes acryl methyl, acryl ethyl, acryl propyl, acryl i-propyl, acryl n-butyl, acryl i-butyl, acryl t-butyl, acryl n-hexyl, acryl octyl, acryl 2-ethylhexyl, and acryl lauryl, the same as a case of the co-polymer.

[0017] The fluororubber includes VDF—HFP, VDF—CTFE, PTFE—P, VDF—PFVE, TFE—PFVE, FVMQ, and VNF (referred to “Plastic Encyclopedia” p509, Asakura).

[0018] It is possible in the present invention to employ a wide range mixture ratio of polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber, and PMMA. Preferable weight ratio of the elastmer to the PMMA is a range of 2 to 30 wt. %, and more preferable ratio is a range of 5 to 15 wt/%. Because the denture having mixture ratios of less than 2 wt. % or more than 30 wt. % show relative poor toughness or obstruction to PMMA properties.

[0019] The invented denture fabricated of injectionable PMMA is given a tone of similar color to capillary and molds in oral mucuous membrane, by adding red, brown or yellowish white dyes, pigment or dyed fibers. Furthermore, it is possible to optionally add inorganic fillers such as calcium oxide, titanium oxide or hydroxyapatite. The dyed fiber includes natural, chemical or synthetic fibers having heat-resistant properties, in which the fibers are preferable to show heat stability of injection temperature in a range of 200 to 270° C., easily dying and adhesion with PMMA. And it is possible to choose cotton, rayon, polyacrylonitrile, nylon 66, polyimide and PVA as the above fiber.

[0020] The denture fabricated by injecting PMMA pellet cohered with red dyed fiber, looks like a tone of similar color to capillary and molds in oral mucuous membrane, because red dyed fiber uniformly disperses throughout molded denture.

[0021] Preferable mixture ratio of the red dyed fiber to the PMMA pellet is a range of 0.01 to 10 wt. %, and more preferable ratio is a range of 0.1 to 0.5 wt/%. Because the denture having mixture ratios of less than 0.01 wt. % or more than 10 wt. % show insufficient coloring or obstruction to PMMA properties.

[0022] Preferable diameter and length of the fiber are ranges of 1 to 30 μm and 0.5 to 3 mm, and the injected denture fabricated of the above fiber looks like a tone of similar appearance to capillary and molds in oral mucuous membrane, because of uniformly dispersing and maintaining fiber shape after injection.

[0023] A method for producing the tough denture, is composed of following steps;

[0024] step 1 ; polymerizing the polymethyl-metacrylate

[0025] step 2 ; mixing polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber into the polymethylmetacrylate and pelleting,

[0026] step 3 ; optionally adding red, brown or yellowish white dyes, pigment or dyed fibers, furthermore, optionally adding inorganic fillers such as calcium oxide, titanium oxide or hydroxyapatite,

[0027] step 4 ; purifying the gained pellet,

[0028] step 5 ; drying the pellet in a range of 60 to 120° C. more than 4 hours in order to reduce moisture content until less than 2%, and

[0029] step 6 ; injecting the dried pellet to form denture shape in denture mold in a range of 220 to 270° C.

[0030] Producing method of PMMA is possibly employed the ordinary method, for example, method disclosed in Jpn 5/139925. The denture is usually produced according to above described steps of 2 to 5, but in step 6 of injection, detorioration of PMMA and fiber is kept away from heating up injection temperature until more than 270° C.

[0031] PMMA denture of the present invention is possibly given antibacterial property by adding inorganic antibacterial agent.

[0032] In conclusion, PMMA denture of present invention shows improving safety to living organism and productivity of molding because of excellent mechanical properties and remarkable elution volume decrease after polymerization in comparison with ordinary type denture of heat-polymerized PMMA. Furthermore, it is possible to widely apply to clinical use because of good adaptability in oral and economical advantage.

EXAMPLE

[0033] Details of the present invention are explained by following examples.

[0034] Mechanical properties and eluted volume of dissolved monomer residue after injection molded castings, of examples 1 to 7 and comparative examples 1 and 2 are measured according to ASTM and weight decrease of the castings after dipping and stirring 3 days at 50° C. in methanol.

[0035] Table 1 and 3 show tensile strength, Izod impact strength and bending strain. And table 2 and 4 show the eluted volume according to above described method.

Example 1

[0036] The syndiotactic and atactic PMMA pellets having weight-average molecular weights of about 220 and 280 thousands are mixed each other by a ratio of 50 by 50 wt. %, molded in plaster mold by injector, and fabricated castings.

Example 2

[0037] Copolymer blend composed of syndiotactic PMMA of 90 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 10 wt. % are made to pellet, molded in plaster mold by injector, and fabricated castings.

Example 3

[0038] Syndiotactic PMMA pellet having weight-average molecular weight of 120 thousand, is cohered by red dyed cellulose fiber of 0.2 wt. %, molded in plaster mold by injector, and fabricated castings.

Comparative Example 1

[0039] Methylmeatacrylate of 50 wt. % is mixed with PMMA powder of 50 wt. % having weight-average molecular weight of 460 thousand, made paste, molded in plaster mold, and fabricated castings. TABLE 1 Specimen Example Example Example Comparative Test Item 1 2 3 Example 1 Tensile Strength 82.3 77.8 76.4 74.6 at Break (MPa) Bending 3.5 kgf 1.50 1.56 1.58 1.85 Strain(mm) 5.0 kgf 2.53 2.64 2.75 3.53 Izod Impact Strength 1.75 1.68 1.62 1.54 (kg.cm/cm²)

[0040] TABLE 2 Specimen eluted volume (%) * Example 1 1.96 ± 0.64 Example 2 1.78 ± 0.72 Example 3 1.82 ± 0.60 Comparative Example 1 8.05 ± 0.96

Example 4

[0041] Copolymer blend composed of syndiotactic PMMA of 90 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 10 wt. %, is cohered by legal pigment of Brown No. 201 (fabricated by Kiki Kasei Ltd.) in a ratio of 0.1 parts to 100 parts of the polymer, molded in plaster mold by injector, and fabricated castings.

Example 5

[0042] Co-polymer blend composed of syndiotactic PMMA of 90 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 10 wt. %, is cohered by legal pigment of Yellow No. 205 (fabricated by Kiki Kasei Ltd.) in a ratio of 0.1 parts to 100 parts of the polymer, molded in plaster mold by injector, and fabricated castings.

Example 6

[0043] Co-polymer blend composed of syndiotactic PMMA of 90 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 10 wt. %, is cohered by a mixture composed of 100 parts of the polymer, 0.1 parts of above mentioned Brown pigment No. 201 and 0.4 parts of tribasic calcium phosphate (Wako Ltd.), molded in plaster mold by injector, and fabricated castings.

Example 7

[0044] Co-polymer blend composed of syndiotactic PMMA of 90 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 10 wt. %, is cohered by a mixture composed of 100 parts of the polymer, 0.1 parts of above mentioned Yellow pigment No. 201. and 0.3 parts of Anatase form titanium dioxide (Wako Ltd.), molded in plaster mold by injector, and fabricated castings.

Comparative Example 2

[0045] Co-polymer blend composed of syndiotactic PMMA of 99.9 wt. % having weight-average molecular weight of 120 thousand and n-butyl acrylate of 0.1 wt. % is made to pellet, molded in plaster mold by injector, and fabricated castings. TABLE 3 Specimen Example Example Example Example Comparative Test Item 4 5 6 7 Example 2 Tensile Strength 76.5 76.6 75.7 75.3 74.7 at Break (MPa) Bending 3.5 kgf 1.51 1.57 1.57 1.48 1.84 Strain(mm) 5.0 kgf 2.66 2.70 2.70 2.68 3.51 Izod lmpact Strength 1.79 1.75 1.69 1.71 1.56 (kg.cm/cm²)

[0046] TABLE 4 Specimen eluted volume (%) * Example 4 1.80 ± 0.52 Example 5 1.90 ± 0.77 Example 6 1.78 ± 0.74 Example 7 1.81 ± 0.63 Comparative Example 2 1.82 ± 0.74 

What we claim is:
 1. A tough denture which comprises solid polymethyl-metacrylate as a main component, being added polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber, and is fabricated in a process of being mixed and injected into a denture mold.
 2. The tough denture of claim 1 , in which the polymethyl-metacrylate is composed of a blend of syndiotactic and atactic PMMAs, and forms stereo complex.
 3. The tough denture of claim 1 , in which a weight-average molecular weight of the polymethyl-metacrylate is in a range of 100 to 300 thousand.
 4. The tough denture of claim 1 , in which the polyacrylate rubber is composed of a co-polymer fabricated by co-polymerizing any one of ethylacrylate, butylacrilate, or 2-ethylacrylate, and cross-linkable vinyl monomer.
 5. The tough denture of claim 1 , in which red dyed fiber is added into the polymethyl-metacrylate.
 6. A method for producing the tough denture, which is composed of steps; a step of polymerizing the polymethyl-metacrylate claimed in any claims 1 to 5 , a step of mixing polar elastomer selected from a group of polyacrylate rubber co-polymer, methylmatacrylate-alkylacrylate-styrene ter-polymer, and fluororubber into the polymethyl-metacrylate and pelleting, step of optionally mixing the red dyed fiber with pellet, step of purifying the gained pellet, and step of drying the pellet in a range of 60 to 120° C. more than 4 hours in order to reduce moisture content until less than 2%, and a step of injecting the dried pellet to form denture shape denture mold in a range of 220 to 270° C. 